It would be good/better to have specific nits while selecting the HDR slider values, so that we can match our displays easily.
Alternatively, if you dont feel like changing the current sliders you can add example HDR images while changing them. Similar to how Baldur’s Gate 3 or Dragon’s Dogma 2 works.
As others have stated - when switching to exclusive fullscreen the HDR breaks, I suppose it fails to intialize properly (since it looks like HDR content being played on a non-HDR display).
For me, saving settings and restarting the game fixed this issue.
Finally, I found that having the game’s HDR off and forcing Windows auto-HDR made it look better. If anyone wants to try, google “ledoge/autohdr_force” for the autohdr_force app.